Police Superintendent Garry McCarthy told reporters Thursday the slaying was the result of two gangs fighting. He adds the father isn't cooperating with the investigation.

But the child's father, Pierre Stokes, says he's answered every question police asked him. He hasn't talked about whether he's a gang member but has said he disagrees with authorities' characterization.

Tyshawn Lee was shot in the head and back Monday in a neighborhood on the city's South Side.

Earlier this week, police questioned and released a man they called a “person of interest,” WGN reports. The man turned himself in Wednesday, accompanied by attorney Sam Adam Jr.

Police have executed several search warrants in the investigation, but refuse to release details.

A $35,000 reward is being offered for information leading to the capture of the boy's killer.